CMP is a highly heterogeneous peptide due to a variety of glycosylation patterns and different extents of glycosylations by galactosamine, galactose and o-sialic acid. For this reason CMP does not have a single charge but in reality a distribution of charges exists.
CMP is a unique, naturally occurring peptide that contains no Phe. CMP is e.g. formed during cheese-making when chymosin specifically cleaves κ-casein between the 105 to 106 amino acid residues. Para-κ-casein (residues 1 to 105) coagulates, forming cheese curd, while CMP (residues 106 to 169) remains in the whey. CMP is the 3rd most abundant protein in sweet whey, after β-lactoglobulin (BLG) and α-lactalbumin (ALA).
The lack of Phe makes CMP an interesting protein source for persons suffering from phenylketonuria (PKU).
Several attempts to isolate CMP from whey have been described in the prior art.
U.S. Pat. No. 5,278,288 discloses a method for producing CMP, wherein a cheese whey is subjected to cation exchange and the non-bound fraction is subsequently subjected to ultrafiltration at low pH, whereby the monomeric CMP and other impurities are isolated in the ultrafiltration permeate. The pH of the resulting permeate is finally adjusted to pH 7, which leads to the formation of CMP oligomers, and the CMP oligomers are concentrated by ultrafiltration. The Phe-content of the resulting composition is not mentioned in U.S. Pat. No. 5,278,288.
WO 99/18808 discloses another method of recovering CMP. More specifically, WO 99/18808 describes a process where cheese whey is subjected to two ion exchange steps of opposite polarity performed in sequence. The above-mentioned U.S. Pat. No. 5,278,288 is discussed in the background section of WO 99/18808, and here it is mentioned that the CMP recovery of the method of U.S. Pat. No. 5,278,288 is uneconomically low.
WO 98/14071 discloses a method of producing CMP-compositions. This method involves subjecting cheese whey to an anion exchange process and subsequently to a second ion exchange process which may be a cation or anion exchange process. The resulting CMP composition is said to have a Phe-content of at most 0.5% (w/w) relative to the total amount of amino acids determined after protein hydrolysis by hydrochloric acid.